I have already loaded a large list of IP addresses yet there are spam users registering all the time.

One thing I can do is I can check the bounce mail to find the username and can pipe bounced mails to a php script and immediately delete that user, but I have not got any bounce back from hotmail or some other email clients.

So this way it will catch hold of a certain percent of spam users but there are still a huge amount of users spamming.

Great idea, depending on how long it works. To help future readers of this answer, can you edit this to mention which files you had to edit so that legitimate visitors would still be pointed to the correct URL?
–
joshuahedlundDec 15 '11 at 16:23

i have updated my answer as per your request. if i am being attacked again then i will again change my files and will allow redirection from searching engines using htaccess buy conditioning whether bots are accessing those pages.
–
Jayapal ChandranDec 16 '11 at 9:51

and lately i had been thinking of writing a forum of my own...
–
Jayapal ChandranSep 11 '14 at 7:42

i have updated that and cloudflare said it would take max of 24 hours for the dns to get updated... besides i installed the mod keycaptcha from www.keycaptcha.com . do you have any idea... in the admin it instructed me to update their api key and javascript code when i submitted the form i get 406 not acceptable.
–
Jayapal ChandranNov 28 '11 at 12:16